docs: finish instantiating the RSR docs skeleton

[hyperpolymath]

What

This repo was minted from the RSR template and got a docs skeleton
(docs/architecture.adoc, docs/contributing.adoc, docs/usage.adoc,
docs/troubleshooting.adoc, ADR 0001) adopted wholesale in #11, but the
skeleton was never actually filled in — it still carried <angle bracket> placeholder tokens and generic boilerplate describing a
built/tested software product (just recipes, an HTTP API, Rust
source paths) that has never existed in this repo.

technical-notes is, in fact, a documentation archive: short citable
technical notes, individually deposited on Zenodo with a DOI (see
README.md). No source code, build system, or test suite. This PR
rewrites the process docs to say that, plainly and minimally, instead
of describing a fictional product.

Changes

• docs/architecture.adoc, docs/contributing.adoc, docs/usage.adoc,
  docs/troubleshooting.adoc: replaced unfilled placeholders and
  fictional software-product content with a truthful description of
  the actual publishing/citation process. Fixed the stray
  :revdate: 2026-MM-DD placeholders. Dropped a dead link to a
  nonexistent SECURITY.md.
• ARCHITECTURE.md, GOVERNANCE.md, MAINTAINERS (repo root): these
  were 100% unedited generic scaffold text (mentions src/, tests/,
  scripts/, config/, "public APIs", multi-maintainer RFC process)
  that never matched this repo. Rewritten to match reality: single
  maintainer, no software architecture.
• MAINTAINERS, .github/CODEOWNERS, .github/funding.yml: these
  pointed at @metadatastician, the RSR template's literal default
  owner value, never swapped for this repo's real owner. Corrected to
  @hyperpolymath, which matches every commit author and existing
  SPDX FileCopyrightText in this repo.
• mise.toml: trimmed from a full generic multi-language toolchain
  list (node/python/go/java/rust/…) down to what this repo actually
  needs — git and typst (for reproducing a note's rendered PDF).

Not touched

flake.nix, .tool-versions (not present), .editorconfig,
.gitattributes, .gitignore — excluded per estate convention.
README.md's CC-BY-4.0 licence line for note content was left
alone: it's consistent with .zenodo.json and is a separate,
intentional licence from the MPL-2.0/CC-BY-SA-4.0 covering this repo's
own tooling/process docs.

Not applicable here

No literal {{...}} mustache placeholders, scripts/validate-template.sh,
tests/e2e/template_instantiation_test.sh, justfile, or .zig
sources exist in this checkout, so those parts of the standard
instantiation cure don't apply to this repo.

Verification

• grep -rn '{{' . (excluding GitHub Actions ${{ }} expressions):
  clean.
• grep -rn 'metadatastician': clean.
• grep -rn 'MM-DD': clean.
• Remaining <...> placeholders in docs: only one intentional
  notational use (zenodo.<version> describing the DOI format, not
  an unfilled field).
• All three .github/workflows/*.yml files parse as valid YAML
  (python3 -c "import yaml; yaml.safe_load(...)"), each with at
  least one job — unchanged by this PR, verified as a regression
  check.

Co-Authored-By: Claude Opus 5 noreply@anthropic.com